1. Technical Field
The present invention relates to a liquid droplet ejecting head and a liquid droplet ejecting apparatus. More specifically, the present invention relates to a piezoelectric element for a liquid droplet ejecting head and a liquid droplet ejecting apparatus with improved durability.
2. Related Art
In liquid droplet ejecting apparatuses currently known in the art, such as ink jet printers, there are liquid droplet ejecting heads equipped with piezoelectric elements which are configured to eject liquid droplets of ink or the like. The liquid droplet ejecting heads change the pressure within a pressure chamber formed below an oscillating plate by allowing the piezoelectric element to change the shape of the oscillating plate in response to driving signals and the like. With such a configuration, it is possible to eject liquid droplets supplied through nozzle orifices into the pressure chamber. In some configurations, the liquid droplet ejecting have having a structure in which a piezoelectric layer is covered by an upper electrode in order to protect the piezoelectric layer of the piezoelectric element which is often subject to deterioration due to external factors such as humidity (for example, see Japanese Patent Document JP-A-2009-172878 (FIG. 2)).
In the case where the upper electrode structure of the piezoelectric element is adopted as disclosed in JP-A-2009-172878, when the piezoelectric layer is deformed by applying a voltage to the lower electrode and the upper electrode, the opposing upper electrode is stressed by the piezoelectric layer. As viewed from the longitudinal direction of the piezoelectric element, one end of the upper electrode is formed as a free end, while the other end thereof extends up to the outside of the pressure chamber or the piezoelectric body. Therefore, the unbalanced stress is caused by the both ends of the active area defined as an area in which the upper electrode and the lower electrode overlap with each other. Thus there is a problem in that crack tends to occur particularly at the free end side thereof in view of durability.